What of the swinging counterweight configuration? A detailed analysis of this configuration is left for our upper-division mechanics course, but students at the introductory level can appreciate the essential results. Consider the motions of two otherwise identical trebuchets, one with a fixed counterweight, and one with a swinging counterweight. Both counterweights liberate the same amount of gravitational potential energy. However, the fixed counterweight transfers some of this energy into rotational motion as it is constrained to move about the throw arm. The swinging counterweight falls nearly straight down, without significant rotation, and has very little kinetic energy as the projectile is released. The swinging counterweight transfers more energy into rotational kinetic energy of the throw arm and thus the projectile.